# How precisely are pilots expected to be able to read altimeters?

I'm writing a program to practice reading three-hand analog altimeters. How precisely should a pilot be able to read one?

• Not really an answer: many altimeters bounce around a fair amount. The engine makes a lot of vibration. Then, on the flip side, when there's no vibration the altimeter can stick. (On my glider, I have to tap on it to get it to respond for +-20' changes.) Commented Jul 16, 2023 at 13:17
• As precisely as their vision allows? As precisely as they are at reading an analog clock? Commented Jul 16, 2023 at 19:05

Most altimeters have tick marks every 20 feet, so a pilot should be able to read the altitude to 10 foot precision pretty easily.

• Thank you! I made it go in 10-foot increments. kj7rrv.com/altimeter-practice Commented Jul 16, 2023 at 17:50
• @kj7rrv In an airplane with ambient vibration from an engine that breaks down internal stiction of the mechanism, the needle moves smoothly more or less like a sweep second electric clock in a continuous motion. You shouldn't make it move like a quartz clock; it's not realistic at all. You can easily discern 10 ft, half a tick mark. The required accuracy of the instrument itself is +/- 50ft but that doesn't apply here. Commented Jul 17, 2023 at 1:29
• @kj7rrv Looks good. Might be a good idea to have it display some small negative altitudes to keep people on their toes. Commented Jul 17, 2023 at 1:53
• @JohnK so you're suggesting that I make it move smoothly when it shows a new altitude? Commented Jul 17, 2023 at 15:26
• @Chris-RegenerateResponse that's a good idea! Right now it goes 0 to 18000 feet. Maybe change it to something like -300 to 18000? Commented Jul 17, 2023 at 15:27

Altimeter reading precision is not an item on the Airman Certification Standards - formerly known as Practical Test Standards (PTS) - used by the FAA as the grading criteria for checkrides. The ability to hold altitude within certain tolerances during various maneuvers is.

The private pilot (PPL) criteria are +/- 200 feet in cruise and +/- 100 feet in the traffic pattern and most maneuvers. So you need to be able to read the altimeter well enough to judge that.

In practice, as the other answer stated, it's pretty easy to read within 10 or 20 feet on all types of "steam gauge" (moving needle) and digital flight displays I've seen.